1. Field of the Invention
The present invention relates to a wireless communication device and a wireless communication method. More particularly, the present invention relates to a wireless communication device constituting a wireless network for performing communications between wireless communication devices, and to a wireless communication device that can transfer a function of a first wireless communication device functioning as a base station in a wireless network that is already formed, to a second wireless communication device to be newly added.
2. Description of the Related Art
Wireless LAN technologies such as 802.11a, 802.11g, and 802.11n prescribed by the IEEE (The Institute of Electrical and Electronic Engineers) 802.11 task group for developing standards for wireless LAN, are becoming widespread in homes and offices all over the world.
As to the specification of 802.11a/11g/11n, there are two connection formats, i.e., an infrastructure mode using a base station and an ad-hoc mode.
In the infrastructure mode, there are stations that are wireless LAN terminals centering around a base station, and data transmission between one station and another station is performed via the base station. The infrastructure mode is widely applied to environments such as offices and homes. The infrastructure mode is a connection format that is more widespread than the ad-hoc mode that is limited in terms of data transmission speed and security.
Meanwhile, according to technology trends in recent years, there are increasing types of communication devices in which a wireless LAN communication function is installed, i.e., Wi-Fi enabled devices, such as personal computers, mobile phones, digital cameras, keyboards, and headphones. Thus, there is an increased need for transmitting data between various communication devices without using a base station.
Wi-Fi Alliance, which is a business organization for promoting wireless LAN products, announced a draft specification “Wi-Fi CERTIFIED Wi-Fi Direct” for directly communicating between Wi-Fi terminals, in October 2009. Subsequently, an official specification Wi-Fi Peer-to-Peer (P2P) Technical Specification Version 1.15 (hereinafter, “Wi-Fi Direct specification”) was announced in October 2010.
The Wi-Fi Direct specification inherits the conventional infrastructure mode, which is a format where wireless communication devices are present in a wireless network formed by a base station, and data transmission is performed between the base station and the terminals, or data transmission between terminals is relayed by the base station. However, an entity of a base station is not provided. One of the terminals in the network serves as a base station and becomes a P2P Group Owner (hereinafter, “group owner”), and the terminals in the network other than the group owner become P2P Clients (hereinafter, “client”). Data transmission is performed between the group owner and the client, or data transmission between clients is relayed by the group owner.
The respective wireless communication devices in a network as Wi-Fi Direct enabled devices are likely to become a group owner, and thus need to include functions of a base station. Functions of a base station are typically installed in a wireless communication device by software.
The method of determining the communication device to operate as a group owner is defined as Group Owner Negotiation (hereinafter, “negotiation”) in the Wi-Fi Direct specification. Specifically, by comparing the values set in the respective wireless communication devices corresponding to Group Owner Intent (hereinafter, “GOI” or generally referred to as a “base station index”) (0 through 15) expressing the degree of the intension to operate as a group owner, the wireless communication device having a large value, i.e., the wireless communication device strongly intending to operate as a group owner, is determined to be the group owner.
For example, as illustrated in FIG. 1, there are two Wi-Fi Direct enabled devices, a wireless communication device 101 and a wireless communication device 102. When the value of the GOI (Group Owner Intent) of the wireless communication device 101 is “8” and the value of the GOI of the wireless communication device 102 is “5”, the wireless communication device 101 having the higher value operates as the group owner.
As described above, in the Wi-Fi Direct specification, two wireless communication devices report their respective base station indices to each other, and the device having the larger value becomes the group owner, and executes functions of a base station in a conventional wireless LAN.
When a new wireless communication device is to join a P2P group (hereinafter, “group”) where a group owner and clients are already present, negotiation is not executed, and the new device sends a connection request as a client to the group owner.
Assuming that in the example of FIG. 1, the GOI value of the wireless communication device 101 is “1” and the GOI value of the wireless communication device 102 is “0”, and as a result the wireless communication device 101 is the group owner. In this case, even if a wireless communication device 103 that is newly joining has the maximum GOI value of “15”, the wireless communication device 101 having a GOI value “1” continues to operate as the group owner.
The GOI value is determined in consideration of aspects such as the processing capability of the hardware and whether there is an interface for connecting the group with a wireless LAN network (concurrent connection).
It is preferable that the wireless communication device having the highest GOI operates as the group owner.
In the Wi-Fi Direct specification, it is possible for a wireless communication device that is newly joining the group, having a high GOI than the others, to perform negotiation with the wireless communication devices in a network that is already formed, and to become the new group owner. However, as shown in FIG. 2, assuming that an existing client 202 is present, and the group owner is switched from a wireless communication device 201 to a wireless communication device 203, the communication of the existing client 202 is cut off.
A technology of continuing communication even if the device serving as the base station is changed to another device as viewed from the client, is described as a roaming technology in Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications 802.11-2007 (hereinafter, “IEEE 802.11 specification”) issued by IEEE. Roaming is a technology for setting a SSID (Service Set Identifier) in advance in plural base stations as a common network ID. When a wireless communication device becomes distant from a base station to which it has been initially connected, and the wireless communication device can no longer detect the base station, the wireless communication device searches for another base station having the same SSID, and when such a base station is found, the wireless communication device connects with the found base station.
As to the roaming technology, patent document 1 describes a mapping table storage unit for storing connection information used for connecting to a base station of a public wireless LAN that is a roaming destination and a mapping table used for generating Web authentication information, and a roaming connection information generating unit for referring to the mapping table and generating connection information and Web authentication information of the base station of the public wireless LAN that is the roaming destination, based on connection information and Web authentication information of a base station of the public wireless LAN specified by the user. Accordingly, the connection information and the Web authentication information of a base station for receiving a roaming service are easily set.
Furthermore, patent document 2 describes that in a storage unit of a wireless LAN terminal, plural MAC addresses corresponding to wireless base stations to which the wireless LAN terminal can be connected are stored in advance. When roaming to a different base station, a communication control unit selects an arbitrary MAC address read from the storage unit, and a wireless communication unit performs an authentication process and a registration process with the wireless base station of the MAC address selected by the communication control unit. Accordingly, the time required for the roaming operation is reduced.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-005011
Patent Document 2: Japanese Laid-Open Patent Publication No. 2009-239513
In both documents 1 and 2, it is assumed that the same SSID is set in plural base stations in advance. Furthermore, it is assumed that when the wireless LAN terminal can no longer detect the base station to which it has been connected, the wireless LAN terminal switches to another base station. Therefore, these technologies do not compare the base station indices expressing the degree to which each wireless communication device may function as a base station, and do not consider transferring to a base station having a higher base station index.